1. Field of the Invention
The present invention relates to an insulating film, and more precisely, to an insulating film having good film properties such as a good dielectric constant and good mechanical properties, to a process for forming the insulating film and to an electronic device having the insulating film.
2. Description of the Related Art
In recent years, accompanied by the progress of high integration, multifunction and high performance in the field of electronic materials, circuit resistance and condenser capacity between wirings have been increased thus causing increase of electric power consumption and delay time. Particularly, increase of delay time becomes a large factor for the reduction of signal speed of devices and generation of crosstalk, so that reduction of parasitic resistance and parasitic capacity are in demand for the purpose of attaining acceleration of devices by reducing this delay time. As one of the concrete measures for reducing this parasitic capacity, an attempt has been made to cover periphery of wiring with a low dielectric layer insulating film. Also, the layer insulating film is expected to have superior heat resistance which can withstand the thin film formation step at the time of mounting substrate production and chip connection, pin attachment and the like post steps and also chemical resistance that can withstand wet process. In addition, a low resistance Cu wiring has been introduced in recent years instead of the Al wiring, and accompanied by this, flattening by CMP (chemical mechanical polishing) is commonly carried out, so that high mechanical strength which can withstand this process is in demand.
Polybenzoxazole and polyimide are widely known for insulating films of good heat resistance. However, since they contain a nitrogen atom of high polarity, they could not form films that are satisfactory in point of the necessary low level of dielectric constant, the water absorption resistance, the durability and the hydrolysis resistance.
In general, many organic polymers are poorly soluble in organic solvent, and a technique of preventing polymer deposition in coating solutions and preventing depositions in insulating films is an important theme in the art. To solve the problems, when the polymers are so modified that their main chain has a folded structure in order to have an increased solubility, then their glass transition point lowers and their heat resistance also lowers, and after all, it is not easy to obtain polymers that satisfy both the intended properties and the solubility.
Also, there has been known a highly heat-resistant resin having a backbone structure (main chain) of polyarylene ether (U.S. Pat. No. 6,509,415) which has a dielectric constant in the range of from 2.6 to 2.7. However, it is desired to further lower the dielectric constant of the resin for realizing high-speed devices. It is also desired not to make a film porous but to make the film have a bulk specific dielectric constant of 2.6 or less, more preferably 2.5 or less.